This description relates to power distribution systems, and, more particularly, to systems and methods for a high-voltage direct current (HVDC) transmission and distribution system control and protection.
As oil and gas fields in shallow waters go dry, producers are tapping offshore fields in deeper waters with oil installations that operate far below the surface of the sea. The typical equipment for such subsea oil recovery and production include gas compressors and various pumps for multiple functions. Electric variable speed drive (VSD) and motor systems are one way to power such equipment directly under the deep water. Therefore, the delivery of electric power from a remote onshore utility grid or power generation is important to secure a reliable production and processing of oil and gas in subsea locations. Typically, the transmission power requirement is approximately one hundred megawatts for medium to large oil/gas fields.
For applications wherein bulk power is transmitted over long distances to offshore locations, alternating current (AC) transmission faces technical challenges, which becomes more significant when transmission distance is in excess of one-hundred kilometers. The significant reactive power drawn from the distributed subsea cable capacitors restrains the power delivery capability as well as increases the system cost.
Direct current (DC) transmission is more efficient over longer distances than AC transmission. Medium voltage (MV) or high voltage (HV) DC transmission typically requires power electronic converters which are capable of converting between HV AC and HV DC. In conventional converter topologies, each switch of the converter is designed to handle high voltages which may range from tens of kilovolts to hundreds of kilovolts depending upon the application needs. Such switches are typically arranged with series connection of several semiconductor devices such as insulated gate bipolar transistors (IGBTs) and thyristors. Another method is to use switches within modules of lower voltage rating and achieving the high voltages required by connecting as many modules in series as the application requires. Due to the special application in subsea, receiving-end converters need to be designed on a modular-basis which is easy to transport, marinize, install, and retrieve.